1. Technical Field
The present invention relates to the manufacture of vehicle occupant restraint systems, and more particularly to a process for recovering alkali metal azide values from waste gas generating material produced during the manufacture of such restraint systems.
2. Description of the Prior Art
Most vehicle occupant restraint systems today use a gas generating material which comprises, as one ingredient, an alkali metal azide. The gas generating material also comprises a reactant for the azide, usually a metal oxide such as copper oxide or iron oxide. The gas generating material may further comprise a water-soluble oxidant such as sodium nitrate. A coating containing potassium perchlorate and other ingredients may be applied to the gas generating material. The gas generating material may also comprise other ingredients, such as bentonite, graphite, and silica.
In the manufacture of the gas generating material, the ingredients are mixed and formed into a desired shape, such as tablets, granules or multi-holed cylinders known as grains. When ignited, the gas generating material produces nitrogen gas. During the manufacture of the gas generating material and the formation of the material into shapes, waste gas generating material is produced. Waste gas generating material can also be produced during handling of the formed shapes of gas generating material, for instance in packaging the shaped material. Further, waste gas generating material can result because of a failure of the grains to pass certain tests.
Alkali metal azides are expensive. The disposal of alkali metal azides is also expensive. A need exists for a method to recover alkali metal azides from waste gas generating material. The method has to be economical and capable of producing an azide product which meets certain specifications permitting reuse of the azide as feedstock in the manufacture of additional gas generating grains. The method also must be capable of processing waste gas generating materials having different compositions. Further, the method has to be capable of producing side streams which contain no azide residuals and which are suitable for either reclaiming or proper disposal. For instance, a waste side stream of a metal oxide or a water-soluble oxidant which is contaminated with sodium azide could have the wrong composition for reclaiming and could be considered hazardous, making it unsuitable for landfill disposal.